PHILOSOPHICAL TRANSACTIONS. 
I. Bakerian Lecture.— On the Variation of the Specific Heat of Water^ 
with Experiments hy a Neio Method. 
By H. L. C ALLENDAR, M.A., LL.D., F.R.S., Professor of Physics at the 
Imperial College of Scie^ice and Technology, London, S. W. 
Received December 5, 1911,—Received in extended form as Bakerian Lecture, February 6, 1912,— 
Lecture delivered February 22, 1912. 
The question of the mode of variation of the specific heat of water is so fundamental 
in calorimetry, there are so few experiments between 50° C. and 100° C., and the 
results in this region obtained by different observers are so discordant, that no 
apology is needed for the publication of new experimental work tending to throw 
light on the subject. But in order to elucidate the points at issue, it will first be 
necessary to review briefly the experimental evidence already in existence, and to 
exhibit the results graphically as an indication of the order of accuracy of the various 
methods. 
A minor difficulty in comparing the residts of different observers arises from the 
fact that they are expressed in terms of different thermometric scales and units, and 
that the reduction to a uniform standard of comparison cannot always be effected 
with certainty. Throughout the present paper, for reasons which have been fully 
explained elsewhere, all heat quantities are expressed in terms of the specific heat of 
water at 20° C. taken as unity. The scale of temperature, t, adopted is that deduced 
from the temperature pt by platinum resistance thermometer by means of the difference 
formula,* 
= 1-50 100) X 10-‘,.(1) 
* Many computers have corrected this formula by assuming values from 414°‘8 C. to 445°‘0 C., or 
even 445°'5 C., for the sulphur boiling-point on the perfect-gas scale. But the recent, experiments of 
Holborn and Henning (‘Ann. Phys.,’ 35, pp. 761-794, 1911) with a quartz-glass bulb give the value 
444° • 51 C. on the perfect-gas scale. They assume the linear expansion coefficient of quartz-glass 
constant and ecpial to 0'54 x 10“'’, which makes the cubical coefficient 1 ’62 x 10“'’. But it appears that 
the linear coefficient vanishes at - 100° C., and is likely to be smaller between 0° C. and 100° C. than at 
higher temperatures. In any case it is unsatisfactory to deduce the cubical coefficient from the linear, 
because the latter is difficult to measure accurately, and may well be different in difierent directions for a 
drawn bulb, especially as quartz-glass cannot be annealed owing to its rapid devitrification at temperatures 
in the neighbourhood of 1,000° C. Direct measurements of the cubical coefficient of a cpiartz-glass bulb, 
by E. J. Harlow (‘Proc. Phys. Soc.,’ Bond., Nov., 1911), employing the method of the mercury weight 
VOL. CCXII.—A 484. B 16.4.12 
